1. Field of the Invention
There is increasing concern with the manner in which drugs are administered. Since in many instances, the effectiveness of the drug is directly related to the concentration of the drug in the bloodstream, both the manner and amount of the drug which is administered, affects the blood level of the drug during an extended period of time. The rate at which the desired blood level is achieved or exceeded will depend upon the nature of the drug, the manner of administration, the dosage, as well of the rate of metabolism. The rate at which a drug will enter the blood stream when administered other than intravenously and the rate at which the drug is metabolized varies widely with individuals. Furthermore, the level of effectiveness will also vary widely with individuals.
It is therefore desirable when administering drugs to ascertain the individual's level of effectiveness, the rate at which this level is achieved at a particular dosage and the time for which the level is maintained. In this manner, the amount of drug which is administered can then be carefully monitored to maintain the desired level. In this way, effectiveness can be assured and side effects minimized.
In order to monitor a drug in a physiological fluid, it is necessary to have sensitive tests which enable the rapid determination of the drug as distinct from any ineffectual metabolites. Thus, the test must clearly distinguish between the drug of interest and compounds of very similar structure. In competitive protein binding assays, antibodies are employed which are prepared by means of antigenic conjugates of derivatives of the drug of interest. In order for the antibodies to be effective, they must be produced in high titer, have a strong binding constant to the drug of interest, and weakly bind to compounds of similar structure.
There is also a need for a reagent which provides a measureable signal related to the amount of drug present in the assay medium. Where antibodies are involved, the reagent must effectively compete with the drug for antibody binding in a reproducible manner and provide for significant changes in the signal with small changes in the drug concentration, over the concentraion range of interest.
Other considerations for a reagent are that it is not affected by materials present in the unknown sample to be assayed or any interfering materials may be removed, an easily determinable signal is obtained, the reagent is stable under the assay condition and has a good storage life and the reagent is readily recognizable by the antibodies for the drug.
2. Brief Description of the Prior Art
Descriptions of competitive protein binding assays may be found in U.S. Pat. Nos. 3,817,837, 3,850,752, 3,690,834, and in an article by Murphy, J. Clin. Endocr. 27 973(1967). Preparation of antigenic conjugates and antibodies for a number of different drugs may be found in U.S. Pat. Nos. 3,888,866, 3,766,162, 3,843,696 and 3,878,187. U.S. Pat. No. 3,875,011 discloses glucose-6-phosphate dehydrogenase conjugates for use in homogeneous enzyme immunoassays. Dahlborn et al, Acta Chem. Scand. 13, 1145(1959) teaches the preparation of 4-amino-2,6-dimethyl-.gamma.-dimethylaminoacetanilide.